Once I had my Exchange 2010 server up and running, I had a need to create a new store. Unfortunately, things didn’t look so great when the store wouldn’t mount after I created the store in the GUI console. There were even some fine error messages in the logs letting me know that Exchange was unable to mount the store. If you search the Web for answers to this problem, you’ll find all sorts of potential solutions and ideas.
Turns out the thing that worked best for me was some patience. Exchange 2010 is deeply ingrained in Active Directory and Active Directory does things at it’s own pace. Sometimes immediately, sometimes in 5 minutes and sometimes in fifteen.
So go ahead and read all those links you found in the great WWW and then after about 5 minutes, go back and try to mount that database again. Chances are, it’ll work just fine.